On average, people with this gene were found to have a lower body mass index. This was unsurprising and is in line with the generally accepted idea that smoking can keep your weight down.

However, the researchers also noticed that for the same body mass index, people with this gene had a greater waist circumference. This suggests that even if you keep your weight down overall by smoking, you may end up with fat being deposited around the stomach, a condition known as ‘central adiposity’. Not only would this suggest that adults who smoke either may gradually acquire an ‘apple shape’ or ‘paunch’, but such adults might then increase their risk of developing type 2 diabetes.

Professor Morris said: “When doctors attempt to persuade their patients to stop smoking, one barrier those patients face is a fear of weight gain. In the short term, the average smoker is right to be concerned about this. However, continuing to smoke may not necessarily result in weight control in the right parts of the body, and if so may in fact increase the risk of diabetes.”

The findings were based on 29 studies across the world involving 150,000 people who either smoked, used to smoke or have never smoked.

If these findings are confirmed in future research, a tendency for smokers to acquire an ‘apple shape’ due to increasing central adiposity might provide a novel health promotion message to encourage smokers to quit smoking, the researchers said.